Double hybrids and need to tag SCF functional
This is partly related to #340: many double hybrids are designed to work perturbatively. For instance, the XYG3 double hybrids are designed for B3LYP orbitals, while wB97M(2) is a correction on top of wB97M-V orbitals.
These pairings should be available directly from libxc, since otherwise the pairings need to be implemented separately in all codes.
@hyllios opinions on how to accomplish this?